Impingement and composition enhanced infrared flare



W. LAI

IMPINGEMENT AND COMPOSITION ENHANCED INFRARED FLARE Filed Feb. 12, 1968United States Patent O M 3,485,169 IMPINGEMENT AND COMPOSITION ENHANCEDINFRARED FLARE William Lai, Los Altos, Calif., assignor to the UnitedStates of America as represented by the Secretary of the Air Force FiledFeb. 12, 1968, Ser. No. 704,739 Int. Cl. C06d 1/10 U.S. Cl. 102-37.8 5Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Thisinvention relates generally to infrared flares and, more particularly toan impingement and composition enhanced infrared flare.

There has been a recent tendency to supplement radar detection andguidance systems with infrared or IR systems. Sources of radiation inthe infrared spectrum are useful as target devices in testing equipmentand training personnel in weapons having infrared sensitive homingmechanisms.

For the purpose of training personnel and development of new equipment,infrared flares, which can simulate the IR output from various thermalengines, are required. The infrared flares may be attached to the wingsof target drones which are remotely controlled, or the flare may bepropelled by rocket to high altitudes and suspended at the peak of itsascent by parachute. The flare may be balloon-dropped from aircraft orcarried by a manned plane to trained detection equipment operators.

Initially, infrared flares were of pyrotechnic compositions which weretowed in appropriate targets by high performance aircraft. This type offlare, however, left much to be desired, the two principal drawbacksbeing their inability to be stopped and restarted and theirinflexibility to adjusting the characteristics of the flare. Therefore,the application of a hybrid combustor for the purpose of circumventingthe two problems was introduced. Although the hybrid combustor flareappeared to satisfy past requirements, it has become desirable toproduce greater enhancement in the radiation of present day infraredflares, While maintaining the restartability and throttleabilitycharacteristics of the hybrid combustor.

SUMMARY OF THE INVENTION The `present invention is an infrared flarewhich incorporates into a single compact package radiation enhancementby impingement and compositional effects, and also restart andthrottling capabilities.

The present invention uses a hybrid combustor. Therefore,restartability, throttleability and other capabilities unique to hybridsapply, The high temperature combustion products generated in themixer-nozzle section of the hybrid combustor flare flow out of anannular nozzle and stagnate at the axis of the abovementioned section.The rear side of the stagnated flame impinges on an impingement blocklocated adjacent the nozzle At steady state, the heated impingementblock will add to the continuum in the flame spectrum. In addition, thehigh temperature flame will also ablate the block, thus en- 3,485,169Patented Dec. 23, 1969 hancing the flame by altering its composition.Thus, this new flare enhances the radiation of the flame by (l)impingement effects which may be separated into that due to stagnationof the flow and that due to heating of the impingement block, and (2) bycompositional effect arising primarily from ablation of the impingementblock. The chemical composition of the impingement block can be chosento enhance various regions of the spectrum.

It is therefore an object of this invention to provide an infrared flarewhich has radiation enhancement by impingement.

It is a further object of this invention to provide an infrared flarewhich has radiation enhancement by composition.

It is another object of this invention to provide an infrared flarewhich has all the unique features of a hybrid combustor, such as restartand throttling capabilities.

It is still a further object of this invention to provide an infraredflare which has a large radiating area.

It is still another object of this invention to irovide an infraredflare which is made in removable sections so that most of the hardwareis reusable.

It is yet another object of this invention to provide an infrared flarewhich is economical to produce and which utilizes conventional,currently available components that lend themselves to standard massproduction manufacturing techniques.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWING The figure of the drawing represents afragmentary side elevational view of the infrared flare of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figure, theinfrared flare 10 is made up of a hybrid combustor 12, having thecharacteristics of restartability and throttleability. The combustor 12is made up of an oXidizer section 14 and a mixernozzle section 16.

The mixer-nozzle section 16 has a cylindrical compartment therein whichcontains a solid fuel 20. Although only one compartment is shown in thedrawing any suitable number may be used. The solid fuel 20 is composedof any suitable base such as castable rubber or methylmethacrylate orthe like, The mixer-nozzle section 16 is further defined by a pluralityof ports 22 located adjacent the solid fuel 20 and terminating in anozzle 24.

Although only two such ports 22 are shown, any suitable number rnay beused, or the plurality of ports may be replaced by a single cylindricalport. The entire inner portion of the mixer-nozzle section 16 is linedwith a suitable insulatory material, such as ceramic-coated material 25.

Adjacent the solid fuel 20 and proximate the nozzle 24 is an impingementblock 26. The impingement block 26 in adjustably mounted by any suitablemeans, such as mounts 28 on an insulated support member 27 in the rearportion of the mixer-nozzle section 16. The block 26 is composed of anysuitable material, such as polymethylmethacrylate and potassium nitrate.In order to further enhance the emissivity the following additives maybe used in the block 26: aluminum, magnesium, silicon, carbon, camphor,polyethylene, Teflon or polystyrene, depending upon the desired IRspectrum of the flame emanating from the nozzle 24. The ports 22continue past the sides of the impingement block 26 before exitingthrough nozzle 24.

The oxidizer section 14 contains therein any suitable oxidizer, such asgaseous oxygen which is -underconstant pressure. The oxidizer section 14further includes a plurality of valves 30, equal to the number of ports22, or a single valve in the case of a single cylindrical port.Alternatively, a plurality of valves may be spaced around thecylindrical port.

The mixer-nozzle section 16 and the oxidizer section 14 are removablymounted to each other by any suitable fastening means, such as clamps 32and sealing means 34. In this manner, either the oxidizer section 14 orthe mixernozzle section 16 may be readily interchanged with another suchsection. The oxidizer, such as gaseous oxygen, flows under pressurethrough valves 30 and into the ports 22 in the mixer-nozzle section 16.The high temperature combustion products generated in the mixer-nozzlesection 16 flow out of the annular nozzle 24 and stagnate at the axis ofthe mixer-nozzle section 16. The upstream side of a stagnated llame 36impinges upon the downstream side of the impingement block 26.

At steady state the heated impingement block 26 Will add to thecontinuum in the flame spectrum. ln addition, the high temperature flame36 will also ablate the block 26, thus enhancing the flame -by alteringits composition. Thus, the flare of the instant invention enhances theradiation of the flame by (1) impingement effects, and (2) compositionaleffect arising from ablation of the irnpingement block.

MODE OF OPERATION Referring again to the figure, the infrared flare 10of this invention utilizes the restartability and throttleability of thehybrid combustor 12 which is designed to supply an oxidizer, such asgaseous oxygen to a solid fuel. The gaseous oxygen is under constantpressure whereby it iS injected into ports 22 of the mixer-nozzlesection 16.

Operation of the infrared flare 10 is initiated in an injector section(not shown) wherein an oxidizer rich mixture of the oxidizer and agaseous fuel, such as propane, is ignited by a spark to generate a hotgas which produces the initial vaporization of the fuel 20. The startingdevice 1 is then terminated after which time combustion of the solidfuel is sustained by the gaseous oxidizer. Additional oxidizer may beintroduced into the hot combustion gases in the mixer-nozzle section 16by regulating valves 30, accordingly, thus further controlling theapplicable burning parameters. A coolant, such as water, (not shown) iscontinuously circulated in a conventional manner through themixer-nozzle section 16 to provide cooling protection for the systemshardware.

In accordance with the instant invention the radiant intensity of theexhaust flame 36 of the infrared flare 10 is enhanced by the judiciousadjustment of the motor parameters, which include propellant compositionand jet impingernent.

The infrared flare exhaust flame 36 will thermally degrade andmechanically erode, that is ablate the impingement block 26 of theinstant invention which is mounted in the path of the exhaust. T heblock-26 further obstructs the flow of the flame 36 and hence gives riseto pressure or shock waves in the exhaust. Thus, depending upon thecomposition, configuration and orientation of the impingement block 26in the exhaust, radiation may be enhanced by (1) an increase ineffective emissivity as a result of particles introduced by ablation,(2) an increase in effective emissivity as a result of local densityincrease due to presence of pressure or shockwave, (3) an increase inlocal temperature due to the presence of pressure and shockwaves, and(4) additional after-burning of ablative products.

I claim:

1. An infrared .flare having the characteristics of restartability andthrottleability comprising a combustor, said combustor including anoxidizer section and a mixernozzle section, said mixer-nozzle sectionhaving a compartment therein containing a solid fuel, a port located insaid compartment and adjacent said solid fuel and terminating in anozzle, said oxidizer section having therein a suitable oxidizer underconstant pressure and a valve means, whereby the oxidizer flows throughsaid valve into said port in said mixer-nozzle section generating hightemperature combustion products which flow out the nozzle in the form ofan exhaust flame, and an impingement block of suitable composition whichincludes an additive means for enhancing the emissivity of said flame ismounted in the rear portion of said mixer-nozzle section adjacent saidsolid fuel and proximate said nozzle, whereby the upstream side of saidflame impinging upon the downstream side of said impingement blockthereby enhances the emissivity of said flame.

2. An infrared flare as defined in claim 1 wherein said compositioncomprises polymethylmethacrylate and potassium nitrate.

3. An infrared flare as defined in claim 2 wherein said additive meansincludes aluminum for,v enhancing the emissivity of said flame.

4. An infrared flare as defined in claim 2 wherein said additive meanscomposition further includes a magnesium additive for enhancing theemissivity of said flame.

5. An infrared flare as defined in claim 1 wherein said oxidizer sectionand said mixer-nozzle section are removably mounted to one another.

References Cited UNITED STATES PATENTS 3,068,641 12/1962 Fox 60-2073,141,294 7/1964 Lawrence et al 60--216 3,144,751 S/l964 Blackman et al.'-251 BENJAMIN A. BORCHELT, Primary Examiner JAMES FOX, AssistantExaminer

